Ever dreamed of owning a private island? Just such an opportunity, in the form of Mark Island, has popped onto the market right off the coast of Maine. An investment of $2.3 million will net your clients a 3-bedroom, 2-bathroom property with solar power and a personal pier. The island is also home to the historic Winter Harbor Lighthouse, which has been looked after by previous owners of the island over the past 75 years.